- Home
- Conferences
- Conference Proceedings
- Conferences
11th SAGA Biennial Technical Meeting and Exhibition
- Conference date: 16 Sep 2009 - 18 Sep 2009
- Location: Swaziland, South Africa
- Published: 16 September 2009
21 - 40 of 157 results
-
-
The Use of Multi-electrode Resistivity Tomography to Map Shallow Old Gold Mine Workings in the Primrose Area, Boksburg
Authors E. Chirenje and S. DiopThe shallow old mine workings along the Main Reef road, in Johannesburg pose a serious hazard to the growing squatter settlements in the area. Recently, there has been documented loss of life and property through subsidence of the ground, in particular, in the Primrose area. In the interest of ensuring public safety, the Department of Mineral Resources and the Ekurhuleni Municipality commissioned the Council for Geoscience to investigate the spatial and depth distribution of the old mine workings in the squatter settlement areas. The idea being to fill the shallow workings (less than 60m), if possible, and certify for settlement (town development) where they are deeper and meet South African civil engineering standards. A survey was carried using multi – electrode resistivity method at Maraisburg along Main Reef road where there are known south dipping shafts, as well as in the Primrose area. The dipole – dipole and Wenner – Schlumberger arrays were used with 10m dipoles. The Res2DINV program was used to model the collected resistivity data. Interpretation of the resulting models show what appears to be locations of old mine shafts, a long tunnel along the strike of the reef and other mine workings. The anomalies are identified at typical first mining level one (approximately 30 m) and some slightly above or below. One can conclude from these results that the method used showed the existence of systematic ‘voids’ in the area, whose geophysical signature can not be associated with naturally occurring geological phenomena.
-
-
-
Where to Next with SQUIDs in Exploration?
Authors Andreas Chwala, Ronny Stolz, Viatcheslav Zakosarenko and Hans-Georg MeyerFirst experiments on using SQUIDs for geophysical purposes are dated back to the early 1970s. But it took more than 20 years until SQUIDs found some commercial application in exploration. Nowadays, SQUIDs have reached a quite mature status in some systems, e.g. rock magnetometers and Transient Electromagnetics (TEM). But many more explorational methods could also benefit from the advantages of SQUIDs, such as high sensitivity and a flat frequency response from DC to up to several MHz.
In this paper I will highlight fields where I see that SQUID could have a major impact in the near future, inter alia Airborne TEM, AFMAG, remote referencing for TEM and Magnetotellurics.
-
-
-
Empirical Correction for Compton Effects in Airborne Radiometric Data
By Henk CoetzeeDuring the development of an ultralight-borne airborne geophysical system, conventional radiometric calibration was found to be impracticable owing to the lack of suitable calibration facilities within range of the base of operations and, in one case, the need to perform Compton stripping on spectra recorded over areas contaminated with anthropogenic radionuclides.
-
-
-
Ground and Airborne Geophysical Surveys Identify Potential Subsurface Acid Mine Drainage Pathways in the Krugersdorp Game Reserve, Gauteng Province, South Africa
Authors Henk Coetzee, Emmanuel Chirenje, Philip Hobbs and Janine ColeFollowing the cessation of underground mining activities in the West Rand Goldfield in the late 1990s all pumping of water from the mine void was halted and water levels were allowed to recover due to ground and surface water inflows. In 2002 the water in the mine void reached the level of the lowest lying shaft and began to decant on surface. This water was of poor quality with low pH and high dissolved solids. Significant effort has been expended since on addressing the impacts of this water on the receiving surface water system. Far less effort has been expended on the groundwater systems in the receiving environment. Ground and airborne geophysical surveys have identified potential subsurface pollution pathways in the Krugersdorp Game Reserve, immediately adjacent to and down-gradient from the West Rand Goldfield.
-
-
-
Application of the Airborne Radiometric Method in Radiation Protection Applications
Authors Henk Coetzee and James LarkinThe airborne radiometric method has been extensively applied to uranium exploration and geological mapping problems since the 1940s, taking advantage of the natural variations in radioelement concentrations in the upper part of the earth’s crust and the information which can be deduced from these regarding surface geology and potentially economic mineralisation. In the process, a number of conventional practices have been adopted, largely regarding calibration and its supporting assumptions. The science of radiation protection looks at the quantification of radiological exposure to human beings, the assessment of the health impacts of these exposures and the development of strategies to minimise these exposures. As a result, the underlying methodologies and supporting assumptions differ, in some cases greatly, from those made in geophysical surveying, potentially resulting in misunderstandings between experts in the two fields. Airborne surveying on its own cannot generally directly quantify the radiological dose to human beings on the ground, although it can be used, given certain assumptions, to estimate ground level exposure rates. It can, however, play a vital role in the location, identification and, to some extent the characterisation of ground sources of radioactivity which could lead to increased radiological doses to the public. The extensive aerial coverage provided by the airborne survey method also offers a unique opportunity for the mapping of potentially radiologically significant sources. While it has traditionally been applied to the mapping of naturally occurring radioactive materials, modern multi-channel airborne spectrometers may also be applied to the search for and mapping of sources containing artificial radionuclides.
-
-
-
The Use of VTEM Data in Geological Mapping and Mineral Exploration in North-eastern Namibia.
Authors M. Combrinck, W. J. Botha and D. HutchinsIn June 2008 a 3310 line-km airborne geophysical survey was flown in north-eastern Namibia for the Geological Survey of Namibia. Time domain electromagnetic data (dB/dt and B-field) as well as magnetic data were acquired with the VTEM system. The survey area is covered with sand and no other detailed information on the sub-surface geology is available. The objectives of the survey were to delineate sub-surface geological units and trends, and to identify possible exploration targets. The TDEM data were processed to obtain three-dimensional conductivity-depth information, decay constant maps and discrete anomaly picks from both the B-field and dB/dt data sets. Together with the magnetic total field data and its derived products (analytical signal, vertical and horizontal derivatives), these were used to delineate geological structures and classify geological units based on their regional setting and physical properties. In addition, targets with exploration potential were identified. The data and some interpretation results are presented in this paper, illustrating the value added to regional mapping and greenfields exploration with airborne TDEM surveys.
-
-
-
Determination of Earth Gravity Field Spherical Harmonic Coefficients Using SLR data
More LessSatellite orbital perturbations resulting from the disturbing-potential (difference between spherical gravitational potential and aspherical geopotential) are in addition to being one of the major sources of orbital perturbations, important indicators of geophysical signals. Determining accurate coefficient values of Earth gravity models is a complex process, usually achieved by combining satellite and terrestrial data, which allow models of high degree and order to be developed. Recently we have developed software that estimates zonal coefficients 2,020,0JJ− as well as and These different coefficients have special applications within interesting scientific questions 21C21.Sranging from relativistic tests of post-Newtonian parameters to fixing the rotation axis of the reference frame. With the development of new models using satellite data (GRACE, GOCE etc.) higher levels of accuracy should be reached, allowing increased potential for more accurate estimates of solve-for parameters of interest, such as SLR station position, other orbital perturbations, geophysical processes and relativistic tests. The new models should still be validated utilising independent techniques such as Satellite Laser Ranging, where particularly the coefficients of lower degree and order affect geodetic satellite orbits. In addition, the ability to estimate gravity coefficients allows determination of trends in the coefficients and validates the software’s force models. A brief description of the method used for the spherical harmonic expansion coefficient is given as well as some results using SLR data to LAGEOS 1 and LAGEOS 2.
-
-
-
Products of Space Geodesy and Links to Earth Science and Astronomy
More LessProducts of Space Geodesy such as Earth Orientation Parameters, polar motion and precise positioning, as well as various applications of these products are of importance to both Earth Sciences and Astronomy. Global geodetic site positions and velocities find application in geodynamics, on a local and global scale, including plate mobility and tectonics, on time scales varying from sub-seconds to millions of years. Precise orbit determination provides information on Earth’s gravity field and changing shape, it also allows calibration of satellite platforms which measure ocean and ice levels. Nuisance parameters such as observable delays due to the ionosphere and atmosphere provide additional information about total electron content and integrated water vapour. Global reference frames on Earth, and celestial reference frames in the universe are maintained and linked to one another, providing unique positioning capability on Earth and in space. Accuracies and precision of techniques and instrumentation are such now that even relativistic parameters can be tested to new levels. Future developments are very promising as the scientific community moves towards implementation of the Global Geodetic Observing System (GGOS), where sub-cm accuracy on global scales is the objective, requiring a factor ten improvement in measurement accuracies and improved models in terms of factors which affect measuring accuracies. The different Space Geodesy techniques will be discussed briefly with examples of their applications, their links to astronomy and the earth sciences, as well as current and future developments, and South Africa’s role currently and in the near future.
-
-
-
Enhancing Circular Features in Potential Field Data using a Generalised Radial Derivative Filter
More LessThe enhancement of potential field anomalies over Kimberlite pipes and meteorite impact sites is of considerable interest, and much work has been done on this subject. This abstract suggests a modification to the generalised derivative to make it act in a radial manner, thus making it useful for the enhancement of near circular features. The filter is applied to gravity data from South Africa.
-
-
-
A Solution-space Approach to the Euler Deconvolution of Map Data
More LessThe application of Euler deconvolution is a common first step in many potential field interpretation projects, however the method is well known for producing large numbers of 'sprays' of solutions which can make the interpretation more difficult. A solution-space approach is taken here, wherein the half-space is discretised into cubes and the number of possible solutions to Eulers' equation that have a particular structural index is counted. This number is a measure of the probability that a potential field source with that structural index is present at that location. The method is demonstrated on gravity data from South Africa.
-
-
-
The Uranium Boom: a Challenge to Geophysical Exploration
By B. CornerThis paper discusses the present and predicted global need for uranium, and the geophysical exploration challenges for the location, mapping, and evaluation of the new deposits needed to address the projected supply shortfall. In 2008, approximately 60% of the world’s uranium production was from Canada, Australia and Kazakhstan. Africa contributed 18.5 %, derived, in order of supply, from Namibia, Niger and South Africa (WNA, 2009). The major requirement for uranium stems from the needs of both developed and rapidly developing countries who do not necessarily have uranium resources of their own but who have expansive nuclear power generation plans, in particular China and India. The potential for Africa to become a leading supplier is immense. The major challenge thus posed to the geosciences is for the refining of resources to proven reserves, and for the location and evaluation of new deposits. In this respect geophysics has played, and continues to play, a leading role in every aspect of the nuclear fuel cycle, including: the direct exploration for uranium, mapping under cover to ever increasing depths, borehole logging for ore reserve evaluation, ore sorting on mines, environmental monitoring, and nuclear waste disposal. In this presentation, some of the main geophysical advances in uranium exploration technology, and the geophysical challenges to uranium exploration, are addressed.
-
-
-
Radon Emanometry Case Studies in Namibia: the Spitzkoppe and Tumas Uranium deposits
Authors B. Corner, Dr. V. Osiyuk, S. Lytvyniuk, A. Kuchmin and D. VerranThe RadonXTM technique uses the principle of adsorption of radon, emanating from buried uranium mineralization, onto activated charcoal. The charcoal is contained within a cartridge which is fitted into the base of an inverted cup, and is buried in the ground for a period of approximately 10 days. The technique differs from alpha-sensitive radon detection systems in that it measures the gamma radiation arising from the daughter products of the adsorbed radon, namely 214Bi and 214Pb. Two case studies are presented, dealing with the detection of partially buried shallow uranium deposits, using the RadonXTM radon emanometry technique. The case studies are sited over the Spitzkoppe and Tumas deposits in the Central Zone of Namibia, comprising uranium mineralization contained in shallow calcretized palaeo-valley gravels buried under a thin cover of calcrete or gypcrete duricrust. The results show that both deposits have clear RadonXTM target anomaly signatures, in large part correlating with the higher grade areas. The technique is thus an effective and essential adjunct to gamma spectrometric surveys in surrounding areas of cover. Although these deposits are shallow, with a depth extent of up to ~20 m, case studies in other areas show an excellent depth of penetration, of 100m or more, under favourable permeability conditions.
-
-
-
A Radon Emanometry Case Study of the Rössing South Deposit, Namibia
Authors B. Corner, H. Sinclair and D. VerranThe RadonXTM technique uses the principle of adsorption of radon, emanating from buried uranium mineralization, onto activated charcoal. The charcoal is contained within a cartridge which is fitted into the base of an inverted cup, and is buried in the ground for a period of approximately 10 days. The technique differs from alpha-sensitive radon detection systems in that it measures the gamma radiation arising from the daughter products of the adsorbed radon, namely 214Bi and 214Pb. The present case study shows that RadonXTM has an improved sensitivity compared to an alpha detection system, in which cups are buried for a period of 30 days. A case study is presented, in which the RadonXTM radon emanometry technique is sited over the Rössing South uranium deposit. The mineralization occurs under a cover varying between 20 and 80 m, within rocks of the Damara Supergroup and associated leucogranites, in the Central Zone of Namibia. The results show that the deposit, blind in terms of a radiometric signature, has a clear RadonXTM target anomaly signature, making the technique an effective and essential exploration tool in areas of deep cover. An excellent depth of penetration, of 100m or more has been quantified elsewhere in the Central Zone, under favourable permeability conditions.
-
-
-
Quantifying the Shared History of Species and Landforms to Decipher Late Cenozoic Co-evolution of Landscape and Biodiversity Across the Kalahari Plateau
Authors F.P.D Cotterill, S. Goodier, C. O’Ryan and M. J. de WitEpisodic uplift and denudation of the Kalahari Plateau, the vast portion of High Africa centred on the Botswanian-Zambezian region, was initiated over 100 mya, a time span that coincides with a long term trend of global cooling from the Late Cretaceous onward. Yet, the origin and subsequent erosion history of this plateau remains poorly known, despite more than 100 years of study (e.g. E. Suess, 1904). The limiting factor in this debate is precise and accurate dating of both the ancient and recent episodic history of Kalahari landscape changes, dates that can then structure tests for controls on epeirogeny and climate change. Geomorphology in particular faces daunting challenges of tracking the evolution of landforms and the formative events that delimit their tenures. These challenges characterize the landscapes of the vast top-surface of the Kalahari plateau. First, because the Kalahari’s veneer –sediments and duricrusts - comprises a condensed sequence that lacks strata suitable for dating, and second, because its gentle topography reflects numerous ancient amalgamated erosion surfaces and a complex history of palaeo-drainage dynamics. Here, we describe results of a new approach to date recent events that affected the Kalahari surface, using detailed studies of the region’s biodiversity and biogeography. We apply methods and concepts of phylogeography to species with distributions confined closely to the landforms we wish to date. We term these species “biotic indicators of landscape evolution” because informative signals of landscape history are preserved in their genomes. We characterise their gene trees to resolve where and when changes modified the distributions of these indicator species. Dating of molecular clocks – on gene trees - confers temporal precision on these evolutionary events that acted on both biota and landform. A synthesis of such biogeographical data can quantify when landforms (e.g. rivers) changed; while phylogeographic studies quantify when these formative events occurred; when populations diverged; and/or experienced demographic expansions. All these signals quantify events that altered landscapes. Relative sensitivity to changes in a landform varies greatly between different species, so their respective phylogeography exhibits corresponding differences in what they can tell us about where and when landscapes changed. We concentrate on aquatic organisms, especially fishes, because they are especially informative biotic indicators, given their sensitivity to habitat changes. Anomalies in fish distributions often reflect relatively subtle changes to drainage systems. We find that Late Cenozoic drainage evolution across the Kalahari Plateau reflects profound genetic structuring of extant fish faunas in its wetlands today. This testifies to river captures and tenures of palaeo-lakes. Conceptualizing this region’s river networks and depocentres as a wetland archipelago provides a valuable framework to synthesize patterns of biotic and landscape evolution. This confers explanatory resolution on geomorphological reconstructions of its history. Phylogeographic studies of selected species are revealing where and when these drainage systems changed. The combined evidence points to the underlying causes of this landscape evolution against which patterns of climate change may be tested.
-
-
-
Proposal for a Lunar Geotechnical GIS
By L. CroukampThe Lunar Mapping and Modelling Project (LMMP), (Cohen, et al, 2008) is a NASA led initiative with the aim to create a single, consistent, uniform, intuitive and easy to use NASA portal that accesses lunar mapping and modelling products, tools and media.
The USGS started with the foundation for such a system, known as PIGWAD (Planetary Interactive GIS on the web analysable Database). It is clear that the nations of the world are going back to the moon in what is termed “The new Race for the Moon”. The USA Government committed itself to billions of dollars for the Constellation programme which is the programme aimed at returning humans to the moon. The proposal currently in planning stages is to have unmanned and manned rover missions to the moon by 2012, the beginnings of an outpost by 2015, and the construction of a manned moon base by 2020. To prepare for the ambitious international plans for advancing lunar research vast amounts of geological and topographical data need to be collected. Geotechnical properties of the lunar surface must be determined for rover mobility, and will also be required to determine construction methods and materials for a permanent moon base. The GIS proposed in this project will contribute substantially to building the base of relevant data required to enhance and support future missions, target generation for mining of materials for the purpose of propellants, oxygen, construction materials and the planning of excursions as well as the construction of a permanent moon base. Envisaged data layers to be collected include but are not limited to: Geology, Topography, Slope angle, Slope aspect, Surface roughness, Excavatibility, Bearing capacity, Soil density, etc. Once the abovementioned data, and other data have been collected and geo-referenced in a coherent GIS it would be possible to do GIS analysis of the various datasets, either separately or in combination. Maps of resources could be created, as well as the most cost-effective paths for excursions, rover missions and travel paths between bases and sampling points. The inherent structure of a GIS allows several permutations of looking at available data.
-
-
-
O- and H-isotope Study of the Cretaceous Koegel Fontein Complex
Koegel Fontein is a 30 km diameter anorogenic igneous complex that intruded Namaqualand gneisses during the initial phase of break-up of Africa and South America. It is notable for the presence of quartz porphyry dykes that formed from low-δ18O magmas. Many of the igneous rocks show petrographic evidence for alteration and have had their δ18O values lowered by fluid-rock interaction at high temperatures. Partial melting and/or assimilation of this material produced the low- δ18O magmas. Whole-rock δD and δ18O values indicate equilibrium with meteoritc water with a δ18O value around -10 ‰, which is abnormally negative given the relatively low latitude at the time of intrusion. A combination of an elevated volcanic edifice and the ‘continental effect’ is the most likely explanation.
-
-
-
Geophysics and the Deep Structure of the Barberton Belt: A Review
Authors Johan de Beer and Edgar StettlerThe Barberton Greenstone Belt has received world-wide attention as one of the classical areas for studying early Archaean rocks and their environments. However, the Barberton Belt has received little attention from the geophysical community. In 1970 Burley and others made the first attempt to estimate the depth extent of the belt using the gravity anomalies in Swaziland. In a somewhat oversimplified analysis they deduced that the gravity anomaly over the belt can be produced by a flat, steep-sided body, outcropping at the surface and extending to a maximum depth of 3.2 km. In 1975 Darracott compiled a Bouguer gravity anomaly map of the area, which showed that the mafic and ultramafic rocks comprising the Onverwacht Group are associated with a positive gravity anomaly of 20 to 30 mgal. Interpretation of this anomaly indicated that the Barberton Greenstone Belt has a probable depth extent of 3 to 4 km, with the possibility of depth-extents reaching 6 km beneath the deeply infolded sediments of the Fig Tree and Moodies Groups in the vicinity of Barberton. In 1988 De Beer, Stettler and others in a study using the DC resistivity and gravity methods showed that the rocks in the Barberton Belt and the surrounding granitoid terrain have distinctive resistivity and density properties. The models based on the integrated data set established that the depth extent of the greenstone belt does not exceed 8 km. The maximum depth extent is always more than 4 km on all profiles modelled. The authors also found large areas of granitic terrain underlain by greenstone material. The three independent studies basically reached the same conclusions. With better coverage and larger data sets, the estimates for the maximum depth extent increased. The results are in agreement with similar studies in other parts of the world. Invariably the geophysically determined depth extent is much less than the geologically determined stratigraphic thickness.
-
-
-
Denudation Rates for Karoo Dolerites in Southern Africa Determined with Cosmogenic Noble Gas Nuclides
Authors J.E. Decker, S. Niedermann and M.J. de WitSouthern Africa displays an anomalously elevated landscape with a modal elevation of approximately 1000 m above sea level, even though the region is not associated with convergent plate boundaries or active rifting. The origin and evolution of this region’s topography may be constrained by determining the rates of surface processes on intermediate timescales (103 – 106 yr) with in situ-produced cosmogenic nuclides. Here we present minimum exposure ages and maximum denudation rates for Karoo dolerite surfaces across southern Africa, based on the cosmogenic noble gas inventories (3He, 21Ne) of pyroxene separates. Our minimum exposure ages for vertical and inclined scarp faces vary from ~20 to ~380 ka. Maximum denudation rates for horizontal surfaces are consistently low, and generally less than 3-4 m/Myr. These low denudation rates are compatible with a currently stable landscape, and suggest that southern Africa’s topography developed under a significantly different tectonic and/or climatic regime.
-
-
-
Large Scale Thrusting Across the Kango Inlier, Cape Fold Belt, South Africa.
Authors M.J. de Wit and S. MooreStructural mapping and analyses of the Table Mountain Group in the Cape Fold Belt along both the northern and the southern margins flanking the Kango Inlier, 10km west of Calitzdorp, reveals km-scale thrust stacks (duplexes) with more than 70% horizontal shortening along the southern boundary between the Huisriver Formation of the Kango Supergroup and the Peninsula Formation of the Cape Supergroup. In addition, 100-1000m scale folding is documented within the overturned Baviaanskloof Formation to the north of the northern boundary of the Kango Inlier in the Gydo Formation along the Gamkapoort section in the Hell. Strain analysis along this section provides evidence that the extensive thrusting predates the ubiquitous upright folding in the Swartberg Mountain range, suggesting that Peninsula Formation allochthons were emplaced across the Kango inlier early during the deformation history of the Cape orogeny.
-
-
-
The International Continental Scientific Drilling program (ICDP) and South Africa: Steps Towards a Deep Drill-hole Through Earth's Oldest Suture Zone & Establishing a Centre of Drilling Technology in Mpumalanga
More LessThere has long been ad-hoc bilateral international co-operation in a number of scientific drilling projects. However, a multi-national continental drilling program, comparable to the successful Ocean Drilling Program (now Integrated Ocean Drilling Program), was established in the mid 1990s after a conference on the establishment of an International Continental Scientific Drilling Program. Since then the ICDP has grown into a ‘mega-project’ institution. The ICDP comprises 21 members. These include 19 countries, the UNESCO and Schlumberger Services Inc. as a Corporate Affiliate. The youngest members are New Zealand and France, who joined in spring 2009. South Africa has been a member since 2006. The scientific aims of the ICDP are interdisciplinary and attempt to cover a broad spectrum of contemporary Earth Sciences in order to discuss how scientific drilling could complement on-going geo-scientific studies, and make it possible to address fundamental, unresolved questions critically relevant to both societal needs and an improved understanding of the Earth and its Lithosphere. ICDP operates across on all continents, including Antarctica, and has more than 50 active drilling projects and proposals for new drilling projects that fall within the general realms of : Climate Change and Global Environment; Impact Structures; Geobiosphere and Early Life; Volcanic Systems and Thermal Regimes; Mantle Plumes and Rifting; Active Faulting, Collision Zones and Convergent Margins; Natural Resources; Deep Earth Observatories. Technology and capacity building spin-offs are huge. Member countries can participate in any of the ongoing/planned drilling projects, and benefit from numerous short-courses and workshops, advice and technical equipment. They may design also their own deep drilling projects and submit proposals to ICDP for funding thereof, and apply for technical assistance. Project proposals are internationally scrutinized by a Scientific Advisory Group (SAG) that makes recommendations to the ICDP Board. I have now been on the SAG as the RSA representative for 3 years. To encourage more active participation of South African researchers and industry scientists, I would like to take this opportunity to share some of my SAG experiences and convey some of the excitement of ongoing drilling projects that range from deep drilling into volcanic magma chambers, active calderas, active faults (San Andreas), subduction zones, lakes for climate and biodiversity changes, impact sites, deep biosphere, biomarkers of ancient life, geothermal energy, deep mines (RSA, USA), hotspot tracks, and others, under very varied conditions from the tropics to the poles. A group of local and international scientists have recently submitted a proposal for a deep (5-10 km) drill-hole in Mpumalanga, and to build around this a rural college for drilling and related S&T. Phase One of this proposal has been accepted by the ICDP Board, and we will host an exploratory workshop soon. I will outline the aims and timelines of this project; ways to get involved, and solicit new ideas.
-